The embodiments of prior arts pertaining to multiplexing method which have been laid open are described as below.
FIG. 1 illustrates the system according to the embodiments of the prior arts and present invention, all communication channels from the primary communication station 101 to the secondary communication stations 111, 112, 113 are synchronized and also orthogonal to each other.
FIG. 2a is a block diagram of the transmitter of the primary communication station which corresponds to the common constituent parts in the embodiments of the prior arts and present invention, FIG. 2b is a block diagram of the transmitter of the primary communication station on traffic channel in the embodiments of the prior arts. The pilot channel 200 should exist per each Sub-Carrier (SC) because it is used as a channel estimation signal for the purpose of initial synchronization acquisition, tracking and coherent demodulation by the secondary communication station, as shown in FIG. 1, and shared by all the secondary communication stations in the area covered by the primary communication station. As illustrated in FIG. 2a, it also provides a phase reference for coherent demodulation by sending the known symbols. The synchronization channel 210 along with the pilot channel 200 is a one-way broadcasting channel that is broadcast to all the secondary communication stations in the area covered by the primary communication station, and the commonly required information by all the secondary communication stations are transmitted from the primary communication station (i.e., time information and the identifier of the primary communication station).
The data from the synchronization channel pass through a convolution encoder 214, a symbol repeater for adjusting a symbol rate 216, a block interleaver 218 for converting bursty errors to random errors and a symbol repeater 219 for matching a transmitting data symbol rate and are then transmitted to a spreading and modulation block, shown in FIGS. 3a–3f. A paging channel 220 shown in FIG. 2a is a common channel used in case of an incoming message to the secondary communication station or for responding to a request of the secondary communication station. Multiple paging channels 220 can exist.
The data transmitted through the paging channel pass through a convolutional encoder 224, a symbol repeater 226 and a block interleaver 228 and passes through an exclusive OR gate 236 together with an output of a long code generator 232 generated by a long code mask 230. The data through the exclusive OR gate 236 is then transmitted to the spreading and modulation block of FIG. 3.
A traffic channel 240 in FIG. 2b is a channel dedicatedly allocated to each secondary communication station for use until the call is completed. When there are data to be transmitted to each secondary communication station, the primary communication station transmits the data through the traffic channel 240. The data from the traffic channel 240 passes through a cyclic redundancy check (CRC) bit attachment block 241 for detecting errors in a specific time unit, or frame, (e.g. 20 ms in IS-95). Tail bit attachment block 242 are inserted into the traffic channel, all of which are “0”, and the data through the CRC 241 pass through a convolutional encoder 244 for ensuring to independently encoding the channel in a frame unit. The data then pass through a symbol repeater 246 for matching its transmitting symbol rate according to a transmitting data rate. After passing through the symbol repeater 246, the data pass through a block interleaver 248 for changing an error burst into a random error. The data passing through the block interleaver 248 are scrambled in a scrambler 256 with use of a pseudo-noise (PN) sequence, generated by passing an output of a long code generator 232 decimated in a decimator 234 with use of a long code mask 250 generated by an electronic serial number (ESN) allocated to each secondary communication station.
A PCB (Power Control Bit) position extractor 258 extracts a position where a command for controlling transmission power from the secondary communication station is inserted in the PN sequence decimated in the decimator 234. A puncturing and inserting block 260 punctures an encoded data symbol corresponding to the inserting position of the power control command extracted by the PCB position extractor 258 among the data symbols scrambled in the scrambler 256 and inserts the power control command, then transmitting the power control command to the spreading and modulation block in FIG. 3.
According to the present invention, the location of the data symbol for multiplexing transmission hopping time can also be determined by using the PN sequence decimated as shown above.
FIGS. 3a, 3b and 3c show an embodiment of a spreading and modulation block according to the prior art.
FIG. 3a corresponds to the commonly used IS-95 system employing BPSK (Binary Phase Shift Keying) as a data modulation method.
FIG. 3b shows the case for spreading I/Q channel transmitting data by employing a different orthogonal code symbol in FIG. 3a. 
FIG. 3c shows the spreading and modulation block employing QPSK (Quadrature Phase Shift Keying) as a data modulation method for transmitting double data rate in comparison to the method in FIG. 3a. FIG. 3c is adapted in the cdma2000® system, which is one of candidate techniques for the IMT-2000 system.
FIG. 3d shows the spreading and modulation block employing QPSK (Quadrature Phase Shift Keying) as a data 20 modulation method for transmitting double data rate in comparison to the method in FIG. 3b. 
FIG. 3e shows a spreading and modulation block, which employs QOC (Quasi-Orthogonal Code) used in cdma2000® system, which is one of candidate techniques for the IMT-2000 system.
FIG. 3f shows the case for spreading I/Q channel transmitting data by employing a different orthogonal code symbol in FIG. 3e. 
In FIG. 3a, signal converters 310, 330, 326, 346, 364 convert logical values “0” and “1” to physical signal “+1”, and “−1” to be really transmitted. Each channel of FIG. 2 passes through the signal converters and is then spread in spreaders 312, 332 by an output of a Walsh code generator 362. Transmission power of each channel is adjusted in gain controllers 314, 334.
All channels from the primary communication station are spread in spreaders 312, 332 by an orthogonal Walsh function from the Walsh code generator 362 allocated to each channel fixedly. The channels are then gain-controlled in the gain controllers 314, 334 and then multiplexed 316, 336 based on orthogonal code division scheme. The multiplexed signals are scrambled at QPSK spreading and modulation blocks 318, 338 by a short PN sequence 324, 344 for the primary communication station identification. Low-pass filters (LPF) 320, 340 filter the spread and scrambled signals. The signal modulated by the carrier passes through a radio frequency (RF) processing block and is then transmitted through an antenna.
In FIG. 3b, signal converters 310, 330, 326, 346, 364, 365 convert logical values “0” and “1” into physical signal “+1” and “−1” to be really transmitted. Each channel of FIG. 2 passes through the signal converters and is then spread in spreaders 312, 332 by each output of two Walsh code generators 362, 363. Transmission power of each channel is adjusted in gain controllers 314, 334.
All channels from the primary communication station are spread in spreaders 312, 332 by an orthogonal Walsh function of the Walsh code generators 362, 363 allocated to each channel fixedly. The channels are then gain-controlled in the gain controllers 314, 334 and then are multiplexed 316, 336 based on the orthogonal code division scheme. The multiplexed signals are scrambled at QPSK scrambling blocks 318, 338 by a short PN sequence 324, 344 for the primary communication station identification. Signals spread and scrambled are filtered by low-pass filters (LPF) 320, 340. The signal modulated by the carrier passes through a radio frequency (RF) processing block and is then transmitted through an antenna.
FIG. 3c is identical to FIG. 3a except the fact that, in order to transmit the signal generated in FIG. 2 to QPSK instead of BPSK, different information data are carried in an in-phase channel and a quadrature phase channel through a demultiplexer 390. Using the demultiplexer 390 and the signal converters 310, 330 enables QAM (Quadrature Amplitude Modulation) as well as QPSK.
FIG. 3d is identical to FIG. 3b except the fact that, in order to transmit the signal generated in FIG. 2 to QPSK instead of BPSK, different information data are carried in an in-phase channel and a quadrature phase channel through a demultiplexer 390.
FIG. 3e shows the case that a QOC mask is used for distinguishing a channel from the primary communication station to the secondary communication stations in FIG. 3c. Orthogonality is not maintained in a code symbol group using different QOC masks but maintained in a code symbol group using same QOC mask. Therefore, the present invention is applied to the orthogonal code symbol group using the same QOC mask, which may maintain the orthogonality.
FIG. 3f like FIGS. 3b and 3d, is identical to FIG. 3e except the fact that, an independent Walsh code generator exists at I and Q channels in order to be able to spread I/Q channel transmitting data through a different orthogonal code symbol.
FIGS. 4a, 4b and 4c is an example of signal diagram in order to explain the multiplexing method which transmits the signals by allocating orthogonal resource at each channel.
When a primary communication station communicates with its secondary communication stations, the transmission data rate transmitted to each secondary communication station can vary with respect to time. For instance, if the highest transmission rate per channel allocated to the secondary communication station by the primary communication station is a basic transmission rate (R), then the average transmission rate can be a variety of forms such as R, R/2, R/4, . . . , and 0, according to the amount of data transmitted from the primary communication station to the secondary communication station at each frame.
FIG. 4a shows the case for matching an instant transmission rate at each frame with the average transmission rate and this method is used in orthogonal code division multiplexing communication system for a forward link such as IS-95.
FIG. 4b illustrates the method for matching an instant transmission rate with the basic transmission rate at each frame by filling up the empty parts with dummy information when the transmitting data at each frame is less than the basic transmission rate.
FIG. 4c shows the method for adjusting the average transmission rate at the corresponding frame according to a rate between the intervals which possess R and 0 as the transmission rates where the instant transmission rate is either a basic transmission rate (R) or 0 (No transmission). The method used in FIG. 4c is not the transmission symbol based ON/OFF like the present invention, but time slot based ON/OFF. The time slot which is a power control period, is used for controlling the average transmission rate at each frame and at the same time maintaining a reference signal amplitude for closed loop power control of a reverse link in IS-95 system. In the IS-95 reverse link, unlike the present invention, the orthogonality between the channels is not guaranteed.
In FIGS. 4a, 4b and 4c, a primary communication station transmits a common pilot channel to the secondary communication stations in parallel, however, since the pilot channel is used as a reference for synchronization, channel tracking, phase estimation and power control, can be transmitted using the time division multiplexing method similar to the Wideband CDMA (W-CDMA) system for IMT-2000 system. In this case, the pilot channel according to the pilot symbol or location of multiplexing is called in various terms including a Preamble, Mid-amble and Post-amble.
FIG. 4d illustrates the frequency division multiplexing method according to the prior arts. A different frequency band is used as a communication channel between the primary communication station and each secondary communication station. The frequency division multiplexing method according to the present invention includes the Orthogonal Frequency Division Multiplexing (OFDM) method of which has been extensively studied for the purpose of a satellite broadcasting. For the case of OFDM, the frequency band for each subcarrier channel is in an overlapped state which has not been completely separated. However, it can be included in the orthogonal resource of the present invention since the orthogonality between the subcarriers is guaranteed.
FIG. 4e illustrates the conventional time division multiplexing method such as the GSM system. The same frequency band is used as a communication channel between the primary communication station and each secondary communication station. However, each time slot within the frame is wholly allocated to the corresponding secondary communication station.
FIGS. 4f, 4g and 4h show an implementation of the frequency hopping method on the conventional frequency division multiplexing method, as shown in FIG. 4d, in order to improve the frequency diversity and security.
FIG. 4f shows the frequency hopping pattern on a time slot basis.
FIG. 4g shows the regular frequency hopping pattern based on a transmitting data symbol unit.
FIG. 4h shows the irregular frequency hopping based on a transmitting data symbol unit.
FIG. 4g illustrates a method that focuses on frequency diversity and FIG. 4h shows a method that emphasizes the security on frequency diversity and protection against the eavesdropping from any unauthorized receivers. In the frequency hopping multiplexing, there exists a fast frequency hopping multiplexing method based on a symbol and part-symbol unit as well as a slow frequency hopping multiplexing method based on a few symbol units.
The methods shown in FIGS. 4f, 4g and 4h can provide the frequency diversity by implementing the time division multiplexing method in FIG. 4e. In reality, the use of the time slot and frequency hopping based on a frame unit for strengthening of the frequency diversity instead of security enhancement in the second generation mobile communication system such as Global System for Mobile (GSM) is optional.
FIG. 4i illustrates the conventional orthogonal code division multiplexing such as IS-95, cdma2000® and W-CDMA. The communication channels between the primary communication station and its secondary communication stations use the same frequency band and all time slots within the frame. The primary communication station allocates a fixed orthogonal code symbol on each channel at the time of a call establishment, and at the time of a call completion, reallocates the released orthogonal code symbol to one of other secondary communication stations where a new call is being requested. Hence, all data symbols within a frame are spread by the same orthogonal code symbol. The configuration of the transmitter of the primary communication station which corresponds to FIG. 4i is given in FIGS. 3a, 3b, 3c, 3d, 3e and FIG. 3f. 
The configuration of a receiver of the secondary communication station, corresponding to the transmitter of the primary communication station according to an embodiment of the prior art given in FIG. 4i, is similar except the despreading parts for FIGS. 3a, 3b, 3c, 3d, 3e and FIG. 3f. Hence, FIG. 5 briefly describes the configuration of a receiver corresponding to the configuration of the transmitter in FIG. 3a. 
The signal received through the antenna passes through multipliers 510, 530 for demodulating the signal with a carrier, low pass filters (LPFs) 512, 532 for extracting, baseband signal and short code generators 520, 540 for descrambling the signal with a sequence same as the PN sequence used in the transmitter. The signal then passes through multipliers 514, 534 for descrambling the received signal and then despreaders 516, 536 for accumulating the signals during a transmission data symbol area. A channel estimator 550 estimates a transmission channel by extracting only pilot channel components from the received signal. A phase recovery 560 compensates for phase distortion of the received signal using an estimated phase. If the pilot channel is time division multiplexed instead of code division multiplexed, then only pilot channel components are extracted by a demultiplexer and the phase changes between intermittent pilot signals can be estimated by interpolation.
FIG. 6 shows a configuration of a receiver for a channel such as paging channel in which a control command for controlling transmission power from the secondary communication station to the primary communication station is not included. Referring to the figure, maximum ratio combiners 610, 612 combine signals passing through the phase compensation to a maximum ratio. If the transmitter performs QPSK data modulation as shown in FIG. 3b, the receiver performs descrambling by multiplexing the signal in a multiplexer 614, performing soft decision in a soft decision unit 616, then decimating an output of a long code generator 622 generated by a long code mask 620 in a decimator 624, and then multiplying the signal through the soft decision unit with a decimated result of the decimator 624. In the present invention, a configuration of a receiver in the secondary communication station for the orthogonal code hopping multiplexing is similar to the configuration in FIG. 6. For the synchronization channel, the descrambling processes 620, 622, 624, 626, 628 using the long code may be skipped.
FIG. 7 shows a configuration of a receiver for a traffic channel in which a control command for controlling transmission power of the secondary communication station is included. As shown in the figure, the phase-compensated signal passes through maximum ratio combiners 710, 712. In case that a receiver performs QPSK data demodulation as shown in FIG. 5, a multiplexer 714 multiplexes an in-phase component and a quadrature phase component in the signal. An extractor 740 extracts a signal component corresponding to the power control command transmitted from the primary communication station among the received signal. The signal from the extractor 740 then passes through a hard decision unit 744 and is then transmitted to a transmission power controller of the secondary communication station. Data symbols except the power control command in the received signal from the multiplexer 714 pass through a soft decision unit 742. A decimator 724 decimates an output of a long code generator 722 generated by a long code mask 720 generated by an identifier of the secondary communication station. The data symbols from the soft decision unit 742 is then multiplied in a multiplier 718 by a result of the decimator 724, so to perform descrambling.
FIG. 8 shows a function of recovering the received signal through the signal processing of FIGS. 6 and 7 from the primary communication station, through block deinterleavers 818, 828, 838 and convolutional decoders 814, 824, 834. In a synchronizaton channel 810, in order to lower a symbol rate, a sampler 819 performs symbol compression for the signals through the soft decision unit by accumulating the signals, which is an inverse process to the symbol repeater 219. The signal through the sampler 819 passes through a block deinterleaver 818. Then, a sampler 816 performs symbol compression again for the signal, which is an inverse process to the symbol repeater 216, before the signal passes to a convolutional decoder 814. The signal after the symbol compression then passes through the convolutional decoder 814, then the data of synchronization channel transmitted from the primary communication station are recovered. In case of a paging channel 820, the signal after the soft decision passes through a block deinterleaver 828 for channel deinterleaving. The channel-deinterleaved signal passes through a sampler 826 for symbol compression according to the transmitting data rate, which is an inverse process of the symbol repeater 226. The signal after the symbol compression passes through a convolution decoder 824 for channel decoding, so the paging channel transmitted from the primary communication station is recovered.
In case of a traffic channel 830, the signal after the soft decision passes through a block deinterleaver 838 for performing channel deinterleaving regardless of a transmitting data rate. The channel-deinterleaved signal passes through a sampler 836 for performing symbol compression according to the transmitting data rate, which is an inverse process to the symbol repeater 246. A convolutional decoder 834 performs channel decoding for the signal after the symbol compression. A tail bit remover 832 removes tail bits of the signal used for independent transmission signal generation in a frame unit. A CRC 831 generates a CRC bit for the transmitting data portion like the transmitter and checks errors by comparison with a recovered CRC after channel decoding. If the two CRC bits coincide, the CRC 831 determines that there is no error and then the traffic channel data are recovered. If the transmitter does not include information about the transmitting data rate in 20 ms frame unit, the transmitting data rate of the primary communication station may be determined by channel-decoding the signals after the independent channel deinterleaving and comparing the CRC bits. A system, which transmits a transmitting data rate independently, just further requires a channel decoding process corresponding to the data rate.
As shown in FIG. 1, the conventional methods used for maintaining the orthogonality between the channels from the primary communication station to the secondary communication station can be classified into four different types.
First, as shown in FIG. 4d, using a frequency division multiplexing method which fixedly allocates an available frequency band of the primary communication station to a secondary communication station at the time of a call establishment.
Second, as shown in FIG. 4e, using a frequency division multiplexing method which fixedly allocates a time slot of the primary communication station to a secondary communication station at the time of a call establishment.
Third, as shown in FIGS. 4f, 4g and FIG. 4h, allocating a controlled frequency hopping pattern to the secondary communication station in order to avoid a frequency selective fading at the time of a call establishment or using a total bandwidth consisted of several sub-carriers in a single secondary communication station at a given time and place like in a military use.
Fourth, as shown in FIG. 4i, spreading the channel to the secondary communication station by allocating an available orthogonal code symbol to the secondary communication station at the time of a call establishment.
Among the four methods described, the common point for the rest of three methods excluding the frequency hopping multiplexing is fixedly allocating orthogonal resources (frequency, time, orthogonal code) to the secondary communication station by the primary communication station. The frequency hopping multiplexing is also used in applications with a sufficient amount of resources mainly for the purpose of security. Therefore, it is not subjected to an efficient use of the resources. Hence, in a case where this method is used, a fixed allocation of a limited orthogonal resources to a channel with a relatively low activity or a variable channel with a transmitting data rate which is lower than the basic transmission rate, makes an efficient use of the resources very difficult.
Therefore, while the prior art allocates the orthogonal resources such as frequency, time and orthogonal code in a fixed manner so as to have a one-to-one relationship between the orthogonal resource and the channel, the present invention, with a little modification of the prior art, performs statistical multiplexing for traffic channels having low activities in consideration of activity of the transmitting data in order to increase the number of channels from the primary communication station to the secondary communication station and the activities of the orthogonal codes, which are limited resources, and eliminates unnecessary channel allocation and release processes in order to decrease buffer capacity required by the primary communication station, data transmission delay and achieves a seamless handoff to the adjacent cells